The present invention relates to a novel positive-working chemical-amplification photoresist composition used in the photolithographic works for the formation of a finely patterned resist layer on a substrate surface in the manufacturing process of semiconductor devices and other electronic products. More particularly, the invention relates to a positive-working chemical-amplification photo-resist composition capable of giving an extremely finely patterned resist layer having an excellently orthogonal cross sectional profile free from skirt-trailing on a substrate surface with high photosensitivity and good pattern resolution even when the substrate surface is provided with a thin undercoating film irrespective of the material forming the undercoating film.
As is well known, the manufacturing process of semiconductor devices in the modern electronic technology almost always involves at least one step of photolithographic patterning work to form a finely patterned resist layer on the surface of a substrate material such as a semiconductor silicon wafer by using a photoresist composition. Namely, the substrate surface is coated with a photoresist composition in the form of a solution followed by evaporation of the solvent to form a dried coating layer of the composition which is patternwise exposed to actinic rays to form a latent image of the pattern to be developed by using a developer solution by utilizing the solubility difference between the exposed and unexposed areas in the resist layer. Photoresist compositions are classified into positive-working and negative-working ones depending on the solubility difference caused in the photoresist layer by the patternwise exposure to actinic rays.
While several different types of photoresist compositions are known and employed in the prior art, it is a trend in recent years that the so-called chemical-amplification photoresist compositions or, in particular, positive-working chemical-amplification photoresist compositions are more and more highlighted by virtue of the extremely fine pattern resolution of 0.25 μm or even finer and high photosensitivity attainable therewith. Along with the trend in the semiconductor devices toward a further and further increased density of integration, however, extensive investigations are now under way to develop a positive-working chemical-amplification photoresist composition capable of giving a patterned resist layer having pattern resolution of 0.20 μm or even finer.
Chemical-amplification photoresist composition is formulated by comprising a radiation-sensitive acid-generating compound and a film-forming resinous ingredient capable of being imparted with an increased or decreased solubility in an aqueous alkaline developer solution by interacting with an acid. The principle utilized there is that the acid released from the acid-generating compound in the exposed areas interacts with the resinous ingredient resulting in an increase or decrease in the solubility of the resist layer to leave a patterned resist layer by the development treatment. By virtue of the catalytic interaction of the radiation-released acid with the resinous ingredient, chemical-amplification photoresist compositions are generally excellent in the photosensitivity and pattern resolution even with a relatively small amount of the acid-generating compound.
In the positive-working chemical-amplification photoresist composition, the film-forming resinous ingredient is imparted by interacting with the radiation released acid with an increase in the solubility in an aqueous alkaline developer solution. A most typical film-forming resinous ingredient in the positive-working chemical-amplification photoresist compositions is a homopolymer of hydroxystyrene monomer or a copolymer thereof with other copolymerizable monomers, of which at least a part of the aromatic hydroxyl groups are substituted by acid-dissociable solubility-reducing groups such as tert-butoxycarbonyl groups, tetrahydropyranyl groups and the like, which are dissociated by interacting with the radiation-released acid in the exposed areas to increase the solubility of the resinous ingredient in the exposed areas.
Turning now to the nature of the substrate surface, on which a photoresist layer is formed by using the photoresist composition of the present invention, it is rather usual that the photoresist layer is formed not directly on the surface of a semiconductor silicon wafer per se but on the surface of a thin undercoating film of a great variety of materials formed on the silicon surface depending on the particular object of patterning. Examples of the materials of the above mentioned undercoating film covering the intrinsic substrate surface include phosphorus-containing materials such as phosphosilicate glass (PSG), boron-containing materials such as borosilicate glass (BSG), boron- and phosphorus-containing materials such as borophosphosilicate glass (BPSG), nitrogen- and silicon-containing materials such as silicon nitrides SiN and Si3N4 and silicon oxynitride SiON for interlayer insulating films and protecting films on a circuit wiring layer as well as semiconductor materials such as polycrystalline silicon (Poly-Si) for gate electrodes and resistance elements. Further, metallic materials such as aluminum, aluminum-silicon-copper alloys, titanium nitride, tungsten and titanium-tungsten alloys are used as a material of electrodes and circuit wirings.
In the manufacturing process of semiconductor devices, a patterned resist layer is formed by the photolithographic patterning method on a substrate provided with a thin undercoating film of a material selected from the above mentioned various materials. When a patterned resist layer is formed from a chemical-amplification photoresist composition on the surface of an undercoating film of a nitrogen-containing material such as silicon nitride and titanium nitride, it is sometimes the case that the patterned resist layer has a cross sectional profile slightly trailing skirts on the substrate surface. Furthermore, when a patterned resist layer is formed on the surface of an undercoating film of PSG, BSG, BPSG and the like, the cross sectional profile of the patterned resist layer is not fully orthogonal but more or less trapezoidal.
Needless to say, the above mentioned non-orthogonal cross sectional profile of the patterned resist layer is very undesirable against subsequent processing steps in the photolithographic patterning work in which extreme fineness of patterning of 0.20 μm or even finer is required. Thus, it is eagerly desired to develop a novel and improved photoresist composition which is free from the above described problems and disadvantages in the conventional photoresist compositions.